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Microsporum gallinae is a fungus of the genus Microsporum that causes dermatophytosis, commonly known as ringworm.[1] Chickens represent the host population of Microsporum gallinae but its opportunistic nature allows it to enter other populations of fowl, mice, squirrels, cats,[2] dogs and monkeys.[3] Human cases of M. gallinae are rare, and usually mild, non-life-threatening superficial infections.[2]
| Microsporum gallinae | |
|---|---|
 | |
| Microsporum gallinae colony growing in petri dish | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Eurotiomycetes |
| Order: | Onygenales |
| Family: | Arthrodermataceae |
| Genus: | Microsporum |
| Species: | M. gallinae |
| Binomial name | |
| Microsporum gallinae (Mégnin ex Guéguen) Grigorakis (1929) | |
| Synonyms | |
|
Epidermophyton gallinae Mégnin (1881) | |
Microsporum gallinae was first identified in 1881 by Megnin from chicken favus,[4] and named Epidermophyton gallinae.[5] It was later transferred from the Epidermophyton genus, and classified in the Trichophyton genus, as T. gallinae.[4]
The identification of rough-walled macroconidia, a hallmark of the Microsporum genus, lead to the dermatophyte being classified as M. gallinae.[1][4] There is still debate about the phylogenetic placement of this dermatophyte, but the accepted name is Microsporum gallinae.[5] Analysis of its DNA sequences by PCR shows M. gallinae is most closely related to Microsporum vanbreuseghemii and Arthroderma grubyi, both are also zoophilic fungi.[3][6]
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Microsporum gallinae is distributed throughout the world, with cases reported in: Europe, the Middle East, South America, North America, Africa and Japan.[2] The fungus seems to be isolated more often in areas with high humidity and temperature.[3]
In culture, M. gallinae produces a white, satiny colony.[7][8] The colony appears flat with radial folds and irregular edges as it grows in culture[7] The colony reverse produces a strong pigmentation that changes from pink to a deep red and diffuses through the growth medium.[5][7][8] Optimal growth of M. gallinae occurs at 26-28 °C,[3] and no special nutritional requirements are necessary for its growth.[9] Additionally, M. gallinae is urease positive.[9]
During sporulation, septate hyphae,[2][7] with macroconidia with tappered tips, and club shaped microconidia are present.[7][8][10] The addition of thiamine or yeast extracts promotes sporulation of M. gallinae.[7] Hair invasion observed in M. gallinae is large spored ectothrix type, meaning that the spores form outside of the hair shaft.[5]
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Microsporum gallinae is a cosmopolitan zoophilic fungi that very rarely affects humans.[10] It obtains nutrients from keratin-rich skin, nails and hair, releasing enzymes during its digestion that elicit a host immune response as seen in ringworm.[11][12] Microsporum gallinae infection is diagnosed by culturing the scrapings from skin lesions.[9]
Chickens
Microsporum gallinae causes a superficial infection[13] that forms white lesions on the wattles and combs of chickens.[1][10] Lesions may spread to the head and neck.[2] The feathers are normally not affected by the dermatophyte, although some feather loss can occur.[1] Roosters and chicks tend to be more susceptible to the infection, with fighting cocks having the highest rates of M. gallinae dermatophytosis.[2] Although, it tends to resolve with treatment, the M. gallinae infection may become chronic.[1] The lesions can also become infected with bacteria, complicating the infection.[1] In some cases, it can resolve naturally without treatment; however, the infection may persist for weeks prior to clearance.[5]
Humans
Microsporum gallinae has been isolated from the scalp, and smooth skin in human populations.[10] Microsporum gallinae infections are most commonly tinea capitis and tinea corporis.[3] Very few human cases of M. gallinae infection have been reported, none of which were life-threatening.[9] Of the reported cases, individuals ranged from 3–96 years old.[3] They had cutaneous lesions on the glabrous skin or the scalp.[3] These localized lesions are frequently accompanied by itching.[2][9] The cutaneous manifestations are very similar to those of Microsporum canis therefore many cases of Microsporum gallinae could have been unreported.[3]
In rare cases, immunocompromised individuals form severe dissemination on the skin, instead of small localized lesions[3] as a result of handling infected animals.[2][9] Only one case of extensive dermatophytosis was reported involving M. gallinae infection of a person with AIDS.[2][3][9]
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The treatment of M. gallinae involves both topical and oral antifungals.[1][3] Topical antifungals, such as: Terbinafine,[3] Tolnaftate,[1] and orally administered Griseofulvin[1][9] have been used successfully to treat M. gallinae infections in humans and animals.
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